Actuator

ABSTRACT

The actuator is used in a pickup device for a drive device of an optical disc. The actuator is positioned opposing to the optical disc to irradiates a light beam from a light source to an information recording surface of the optical disc. The objective lens is fixed at on the lens holder forming the actuator at a position closer to one end thereof. One coil substrate is fixed on one side face of the lens holder in a range from the one end of the lens holder to a center portion of the lens holder, and the other coil substrate is fixed on the other side face of the lens holder in a range from the other end of the lens holder to the center portion of the lens holder. Therefore, near the end of the lens holder on the objective lens side, the coil substrate is not attached to one side of the lens holder, providing a space below the objective lens. By arranging an optical system to guide the light beam to the objective lens via the space, the optical system can be arranged at the same height level as the actuator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pickup device of a disc drive foroptically writing and reading information on an optical disc and, moreparticularly, to a pickup device suitable for a thin disc drive.

2. Description of Related Art

A disc drive for recording information on and reproducing informationfrom an optical disc such as a CD (Compact Disc) and a DVD (DigitalVideo Disc) includes an optical pickup device. In order to accuratelyrecord and reproduce information on and from an optical disc, the pickupdevice performs a focus control for controlling a distance between anobjective lens and an information recording surface of the optical discand performs a tracking control for controlling the objective lens tofollow an information track of the optical disc.

The pickup device directs a laser beam, which is emitted from a lightsource such as a laser diode, to the objective lens by usingpredetermined optical system components, and irradiates the laser beamonto the information recording surface of the optical disc via theobjective lens. Normally, the objective lens is positioned to oppose tothe optical disc. A laser beam from the light source is guided by theoptical system components to a position below the objective lens alongan optical path provided in parallel with the optical disc. Then, thelaser beam is changed its path by a raise-up mirror placed under theobjective lens to a vertical direction, that is, the direction of theobjective lens, and the laser beam reaches the objective lens. Theobjective lens is mounted on a lens holder and coil substrates aremounted on the lens holder. The lens holder is moved vertically andhorizontally with respect to the optical disc by applying drivingcurrent to the coil substrates in a magnetic field formed by the magnetswhich are placed close to each other, so that the focus control and thetracking control are performed. An example of such a pickup device isdescribed in Japanese Patent Laid-Open under No. 2001-229557.

However, in the above-described pickup device, since the coil substratesare mounted on the opposing sides of the rectangular lens holder, theoptical path of a laser beam from the laser light source cannot bearranged at the same height level as the coil substrates in thehorizontal direction. Namely, since the paired coil substrates arepositioned on both sides of the objective lens, the coil substratesbecome obstacles and prevent a laser beam from being guided to theposition below the objective lens at the same height level as the coilsubstrates. For this reason, in the pickup device described in JapanesePatent Laid-Open under No. 2001-229557, for example, the optical path ofa laser beam is placed below the lens holder. Namely, the optical pathis arranged such that the laser beam is directed to the position belowthe objective lens at a lower level than the coil substrates and thendirected to the objective lens by the raise-up mirror.

However, when the optical path of a laser beam is placed at a lowerheight level than the lens holder, the whole height (thickness in thevertical direction) of the pickup increases. For example, in a thindrive device such as a drive device mounted in a notebook-type personalcomputer, a thin pickup device has to be used and thus the above thickpickup device cannot be used.

SUMMARY OF THE INVENTION

The present invention is devised in view of the above-described point,and its object is to provide an actuator for a thin pickup device whichis suitable for use in a thin drive device.

According to one aspect of the present invention, there is provided anactuator including: a lens holder having an upper face for holding anobjective lens and a pair of side faces for holding coil substrates; theobjective lens fixed to the upper face; and the pair of coil substratesfixed to the pair of the side faces, wherein the objective lens is fixedat a position displaced from a center of gravity of the lens holder toone end of the lens holder, and one of the pair of the coil substratesis fixed on one of the side faces of the lens holder in a range from theone end of the lens holder to a center portion of the lens holder, andthe other one of the coil substrates is fixed on the other one of theside faces of the lens holder in a range from the other end of the lensholder to the center portion of the lens holder.

The above actuator is used in a pickup device which is used for a drivedevice of an optical disc. The actuator is positioned opposing to theoptical disc to irradiates a light beam from a light source to aninformation recording surface of the optical disc. The objective lens isfixed to the lens holder forming the actuator at a position closer toone end thereof. One coil substrate is fixed on one side face of thelens holder in a range from the one end of the lens holder to a centerportion of the lens holder, and the other coil substrate is fixed on theother side face of the lens holder in a range from the other end of thelens holder to the center portion of the lens holder. Therefore, nearthe end of the lens holder on the objective lens side, the coilsubstrate is not attached to one side of the lens holder, providing aspace below the objective lens. By arranging an optical system to guidethe light beam to the objective lens via the space, the optical systemcan be arranged at the same height level as the actuator. As a result,In comparison with the case where the optical system is provided belowthe actuator, whole thickness of the pickup device can be reduced, and apreferable pickup device for a thin-type drive device may be provided.

The lens holder may have a mass portion at a side of the other end, andthe mass portion may have a mass larger than a mass of the one end ofthe lens holder. By this, it is possible to correct the shift of thegravity center of the lens holder when the objective lens is fixed nearone end thereof.

The lens holder may include a first stopper provided at the one end anda second and a third stoppers provided at the other end, wherein thesecond stopper contacts a portion of a body mounting the actuator tolimit movement of the lens holder in a focus direction of an opticaldisc, the third stopper contacts the portion of the body to limit themovement of the lens holder in a tracking direction of the optical disc,and the first stopper contacts the portion of the body to limit themovement of the lens holder in both of the focus direction and thetracking direction.

In this feature, at the end of the lens holder on the objective lensside, one stopper can limit the strokes of the lens holder in both focusdirection and tracking direction. Therefore, the lens holder may beformed thinner.

The actuator may further include: an actuator base having a pair ofyokes; and a pair of magnets fixed to the pair of the yokes, whereineach of the pair of the magnets may be positioned opposing to each ofthe pair of the coil substrates. In this feature, by applying a drivingcurrent to the coils on the coil substrates within the magnetic fieldcreated by the magnets, the objective lens can be moved to perform focuscontrol and tracking control.

Each of the pair of the coil substrates may include a tracking coil anda focus coil formed in alignment with each other in a horizontaldirection of the coil substrate, and the coil substrates may oppose toeach other only in areas where the focus coil is formed. Thus, anappropriate magnetic field can be created between the coil substrates,and a space to arrange the optical system may be ensured.

Each of the pair of the coil substrates may include a pair of lands inan area where the focus coil is formed, and the lens holder may furtherinclude connection wires which electrically connect the lands on thepair of the coil substrates. Therefore, the coil substrates can beelectrically connected by short wires within the area in which the coilsubstrates oppose to each other.

Each of the pair of the magnets may include a magnetization patternhaving a boundary area, and an north pole area and a south pole area onboth sides of the boundary area. A vertically extending portion of theboundary area may perpendicularly cross the tracking coil of the coilsubstrate, and a horizontally extending portion of the boundary area mayperpendicularly cross the focus coil of the coil substrate. In thisfeature, the tracking servo and the focus servo can be appropriatelyperformed by the magnetic field created by the magnets and theapplication of the drive current to the coils. The nature, utility, andfurther features of this invention will be more clearly apparent fromthe following detailed description with respect to preferred embodimentof the invention when read in conjunction with the accompanying drawingsbriefly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are diagrams showing the configuration of a pickup deviceaccording to the present invention;

FIGS. 2A to 2C are diagrams showing the configuration of an actuator inthe pickup device of the present invention;

FIGS. 3A to 3C are diagrams showing the relative positions of coilsubstrates and magnets in the actuator;

FIGS. 4A to 4C are diagrams showing a magnetization pattern of themagnets used for the actuator of the present invention;

FIGS. 5A and 5B are diagrams showing the configuration of the coilsubstrates used for the actuator of the present invention;

FIGS. 6A and 6B are diagrams showing the relative positional relationbetween the magnets and the coil substrates;

FIGS. 7A to 7C are diagrams showing the configuration of suspensionwires used for the actuator of the present invention;

FIGS. 8A to 8D are diagrams showing the configuration of a lens holderused for the actuator of the present invention; and

FIGS. 9A to 9C are diagrams showing stroke limitation performed bystoppers formed on the lens holder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the present invention will now be describedbelow with reference to the attached drawings.

FIGS. 1A to 1C show the configuration of a pickup device according to anembodiment of the present invention. FIG. 1A is a top view of a pickupdevice 100, FIG. 1B is a perspective view of the pickup device 100, andFIG. 1C is a bottom plan view of the pickup device 100. As shown inFIGS. 1A to 1C, the pickup device 100 has various components mounted ona body 1. An actuator base 8 is fixed on the body 1, and the actuatorbase 8 supports a lens holder 5 movably in a focusing direction F and atracking direction T by using four suspension wires 10. The lens holder5 has coil substrates 7 a and 7 b mounted on the opposing sides thereofand an objective lens 4 mounted on the top surface.

Magnets 6 a and 6 b are fixed on the body 1 so as to be respectivelyopposed to the paired coil substrates 7 a and 7 b mounted on the lensholder 5. The paired magnets 6 a and 6 b are fixed so as to be opposedto each other, and a magnetic field is created in a space between themagnets 6 a and 6 b in accordance with the magnetization patterns of themagnets 6 a and 6 b. The lens holder 5 having the coil substrates 7 aand 7 b on the sides is placed in the magnetic field created by thepaired magnets 6 a and 6 b. Thus, when a predetermined driving currentis applied to a focus coil and a tracking coil that are formed on thecoil substrates 7 a and 7 b, the lens holder 5 is moved in the focusingdirection F and the tracking direction T due to force generated by thecurrents in the coils and the magnetic field. Due to the movement of thelens holder 5, the objective lens 4 on the lens holder 5 is moved toperform the focus control and the tracking control.

A laser light source 2 is mounted on an end of the body 1. A laser beamemitted from the laser light source 2 passes through an optical path 3,which is constituted by an optical system arranged in the body 1, andreaches the position below the objective lens 4. A raise-up mirror 9 isplaced below the objective lens. The raise-up mirror 9 changes the pathof the laser beam upward and the laser beam passes through the objectivelens 4 upwardly from below. An optical disc is placed above theobjective lens 4, and the objective lens 4 condenses the laser beam onthe information recording surface of the optical disc.

Next, referring to FIGS. 2A to 2C, an actuator of the pickup device 100will be described below. FIG. 2A is a top view of the actuator, FIG. 2Bis a perspective view of the actuator, and FIG. 2C is a bottom plan viewof the actuator. The actuator 50 is a mechanism for moving the objectivelens 4 in the focusing direction F and the tracking direction T, andincludes the actuator base 8, the lens holder 5, the paired magnets 6 aand 6 b, and the paired coil substrates 7 a and 7 b mounted on the lensholder 5.

As shown in FIGS. 1A to 1C and 2A to 2C, the actuator base 8 is fixed onthe body 1 of the pickup device 100. Further, a pair of yokes 11 isformed on the body 1, and the magnets 6 a and 6 b are fixed inside theyokes 11. In the pickup device 100 of the present invention, the pairedyokes 11 are not completely opposed to each other but are displaced fromeach other in the tracking direction T. This arrangement is made toprovide a space for arranging an optical path (optical system) 3indicated by broken lines in FIG. 2A. The magnets 6 a and 6 b aremounted inside of the yokes 11, and hence a magnetic field is created ina space between the paired magnets 6 a and 6 b.

Meanwhile, on the actuator base 8, the lens holder 5 is supported by thefour suspension wires 10. The lens holder 5 is supported by elasticityof the suspension wires 10 so as to be moved in the focusing direction Fand the tracking direction T. The objective lens 4 is mounted on thelens holder 5. By applying driving current to the focus coil and thetracking coil on the coil substrates 7 a and 7 b, which are mounted onthe lens holder 5, in a magnetic field created by the paired magnets 6 aand 6 b, force is applied to the coil substrates 7 a and 7 b as well asthe lens holder 5 integrated with the coil substrates 7 a and 7 b in thefocusing direction F and the tracking direction T, so that the objectivelens 4 is moved with respect to the information recording surface andthe information track of the optical disc.

As clearly shown in FIGS. 2A and 2B, in the pickup device 100 of thepresent invention, the paired coil substrates 7 a and 7 b are laterally(i.e., in the tracking direction T) shifted in the opposite directionsand are not completely opposed to each other in a horizontal direction.This arrangement is made to place the optical path 3 from the laserlight source 2 at the same height level as the magnets 6 a and 6 b andthe coil substrates 7 a and 7 b.

In an ordinary pickup device, paired magnets and coil substrates arealmost entirely opposed to each other in the width direction. Thus, themagnets and the coil substrates cover both sides of an objective lenslike walls and a laser beam cannot be directed to the objective lens atthe same height level. Hence, the optical path of the laser beam has tobe placed at a lower height than the magnets and the coil substrates,thereby increasing the entire thickness of the pickup device.

On the contrary, in the actuator 50 of the present invention, themagnets 6 a and 6 b and the coil substrates 7 a and 7 b are displacedfrom each other oppositely in the tracking direction T. Namely, thepaired magnets 6 a and 6 b are only partially opposed to each other, andthe coil substrates 7 a and 7 b are only partially opposed to eachother. Thus, as shown in FIGS. 2A and 2B, the objective lens 4 partiallyforms a space in the circumferential direction. The optical path 3 isplaced in the space and a laser beam from the laser light source 2 isintroduced to a position below the objective lens 4. With thisconfiguration, it is possible to arrange the magnets 6 a and 6 b, thecoil substrates 7 a and 7 b, and the optical path 3 of a laser beam fromthe laser light source 2 at the same height level, thereby reducing theentire height (thickness) of the pickup device.

FIGS. 3A to 3C show the positional relation between the magnets and thecoil substrates. FIG. 3A shows the arrangement of the magnets 6 a and 6b with respect to the actuator 50, FIG. 3B shows the arrangement of thecoil substrates 7 a and 7 b with respect to the actuator 50, and FIG. 3Cshows the arrangement of the magnets 6 a and 6 b and the coil substrates7 a and 7 b with respect to the actuator 50. Besides, FIGS. 3A to 3Cshow that the magnets and the coil substrates are removed upward fromthe mounting positions. Namely, in FIGS. 3A to 3C, the magnets and thecoil substrates are moved from the illustrated positions in parallel tolower positions and are fixed thereon.

As shown in FIG. 3A, the magnets 6 a and 6 b are fixed inside the yokes11 so as to be opposed to each other. Moreover, as shown in FIG. 3B, thecoil substrates 7 a and 7 b are respectively mounted on the sides alongthe longitudinal direction of the lens holder 5. As already mentioned,the lens holder 5 is movably supported by the four suspension wires 10in the space between the magnets 6 a and 6 b. As a result, as shown inFIG. 3C, the magnet 6 a and the coil substrate 7 a are positioned closeto each other, and the magnet 6 b and the coil substrate 7 b arepositioned close to each other.

FIGS. 4A to 4C are plan views showing the magnets. FIG. 4A shows themagnet 6 a, and FIG. 4B shows the magnet 6 b. The magnets 6 a and 6 bare produced by magnetizing iron pieces of a predetermined size by usinga magnetizing device. With the magnetizing device, illustratedmagnetization patterns are formed on the magnets 6 a and 6 b. As shownin FIG. 4A, the magnet 6 a has the magnetization pattern constituted bya magnetized area 18 a of north pole, a magnetized area 19 a of southpole, and a boundary area 20 a between the areas 18 a and 19 a. Further,as shown in FIG. 4B, the magnet 6 b has the magnetization patternconstituted by a magnetized area 18 b of north pole, a magnetized area19 b of south pole, and a boundary area 20 b between the areas 18 b and19 b.

FIG. 4C shows the positional relation between the magnets 6 a and 6 b.As shown in FIG. 3A, the magnets 6 a and 6 b are fixed respectively onthe yokes 11 so as to be opposed to each other. FIG. 4C shows thepositional relation between the magnetization patterns of the magnets 6a and 6 b in a state in which the magnets 6 a and 6 b are opposed toeach other on the yokes 11. FIG. 4C shows the relative positionalrelation between the magnetization patterns of the magnets 6 a and 6 b,taken from the direction of an arrow 80 in FIG. 3A. The magnet 6 a isindicated by broken lines and the magnet 6 b is indicated by solidlines.

As shown in FIG. 4C, the magnets 6 a and 6 b are partially opposed toeach other and partially has an overlap in the lateral direction whenviewed from the direction of the arrow 80. At this point, in theperspective view taken from the direction of the arrow 80 in FIG. 3A,the north pole magnetized area 18 a of the magnet 6 a and the north polemagnetized area 18 b of the magnet 6 b overlap with each other, and thesouth pole magnetized area 19 a of the magnet 6 a and the south polemagnetized area 19 b of the magnet 6 b overlap with each other. Inaddition, the boundary area 20 a of the magnet 6 a and the boundary area20 b of the magnet 6 b overlap with each other. As a result, asubstantially recessed magnetic field, which corresponds to themagnetization pattern (hereinafter referred to as a “combinedmagnetization pattern”) schematically shown in FIG. 4C, is formed in aspace between the magnets 6 a and 6 b, that is, a space in which thelens holder 5 is placed.

Next, the coil substrates will be described. FIG. 5A is a plan view ofthe coil substrate 7 a, and FIG. 5B is a plan view of the coil substrate7 b. The coil substrate 7 a is a printed wiring board and has a trackingcoil 13 a and a focus coil 14 a formed on the substrate surface.Further, lands 15 a and 16 a are formed on the coil substrate 7 a toestablish continuity with the opposed coil substrate 7 b.

Meanwhile, the coil substrate 7 b is also a printed wiring board and hasa tracking coil 13 b and a focus coil 14 b formed on the substratesurface. Moreover, lands 15 b and 16 b are formed on the coil substrate7 b to establish continuity with the opposed coil substrate 7 a. In thestate being mounted on the sides of the lens holder 5, the focus coil 14a of the coil substrate 7 a and the focus coil 14 b of the coilsubstrate 7 b are substantially opposed to each other.

FIG. 6A shows the relative positional relation between the coilsubstrates 7 a and 7 b in a state being mounted on the lens holder 5.FIG. 6A perspectively shows the relative positional relation between thecoil substrates 7 a and 7 b on the lens holder 5, viewed in thedirection of the arrow 81 in FIG. 3B. The coil substrate 7 a isindicated by broken lines and the coil substrate 7 b is indicated bysolid lines. As shown in FIG. 6A, the coil substrates 7 a and 7 b aremounted on the lens holder 5 with a such relative positional relationthat the focus coils 14 a and 14 b are substantially overlap with eachother, when viewed from the side of the lens holder 5. Further, in thatstate, the land 15 a of the coil substrate 7 a and the land 15 b of thecoil substrate 7 b are opposed to each other, and the land 16 a of thecoil substrate 7 a and the land 16 b of the coil substrate 7 b areopposed to each other. In a state in which the coil substrates 7 a and 7b are mounted on the lens holder in this manner, the opposed land 15 aand 15 b and the opposed land 16 a and 16 b are electrically connectedvia connecting wires 22 (see. FIGS. 3A to 3C). This electric connectionapplies driving current to the tracking coil 13 b and the focus coil 14b of the coil substrate 7 b.

FIG. 6B shows a magnetic field created by the magnets 6 a and 6 b andthe arrangement of the tracking coil and the focus coil in the magneticfield. As shown, the magnets 6 a and 6 b create a magnetic fieldcorresponding to the combined magnetization pattern of a substantiallyrecessed shape (indicated by broken lines) in FIG. 6B. The boundary area20 a of the magnet 6 a shown in FIG. 4A longitudinally penetrates nearlythe center of the rectangular tracking coil 13 a of the coil substrate 7a shown in FIG. 5A. The boundary area 20 b of the magnet 6 b shown inFIG. 4B penetrates nearly the center of the rectangular tracking coil 13b of the coil substrate 7 b shown in FIG. 5B. Further, the boundaryareas 20 a and 20 b of the magnets 6 a and 6 b laterally penetratenearly the center of the rectangular focus coils 14 a and 14 b of thecoil substrates 7 a and 7 b. The lens holder 5 on which the coilsubstrates 7 a and 7 b are attached is placed in the space between themagnets 6 a and 6 b so as to establish such relative positionalrelations.

Next, the arrangement of the suspension wires 10 will be described. Thesuspension wire 10 is made from a linear metal having elasticity, and soon. In the actuator 50 of the present invention, the lens holder 5 issupported by the four suspension wires 10. As shown in FIGS. 1A and 3A,the ends of the four suspension wires 10 are fixed on the actuator base8 and the other ends are fixed on the coil substrates 7 a and 7 bintegrated with the lens holder 5. Thus, the lens holder 5 is placed inthe space between the magnets 6 a and 6 b while being supported by thefour suspension wires 10 in the horizontal direction. By the elasticityof the suspension wires 10, the lens holder 5 holding the objective lens4 can move in the focusing direction F and the tracking direction T thatare perpendicular to the longitudinal direction (jittering direction J)of the suspension wires 10.

FIG. 7A shows the relative positional relationship between the actuatorbase 8, the suspension wires 10 and the lens holder 5. In the presentinvention, in order to place the optical path of the laser beam at thesame vertical level as the coil substrate 7, the two opposed coilsubstrates 7 a and 7 b are mounted on the lens holder 5 with beingshifted in the lateral direction (tracking direction T). Therefore, thesuspension wires 10 are not in parallel with the jittering direction J.Namely, the suspension wires 10 are extended in a direction having apredetermined angle from the jittering direction J, and the ends of thesuspension wires 10 are fixed on the actuator base 8.

Referring to FIGS. 7B and 7C, the above configuration will be describedin detail. FIG. 7B shows the relative positional relation between atypical actuator base, suspension wires and a lens holder. In FIG. 7B, alens holder 121 is supported by four suspension wires 124 from anactuator base 123. It is to be noted that, since FIG. 7B is a plan viewshowing the top of the actuator, only the two upper suspension wires areshown. An objective lens 120 and a pair of coil substrates 122 a and 122b are mounted on the lens holder 121. As shown in FIG. 7B, when thepaired coil substrates 122 a and 122 b are placed on both sides of thelens holder 121 so as to be completely opposed to each other (namely,without the shift in the tracking direction T, unlike the presentinvention), the four suspension wires 10 fixed on the actuator base 8and the lens holder 121 are arranged in parallel with each other.

On the other hand, FIG. 7C schematically shows the relative positionalrelation between the actuator base 8, the suspension wires 10 and thelens holder 5 in the actuator 50 of the present invention. In the caseof the present invention, the coil substrates 7 a and 7 b are mounted onthe sides of the lens holder 5 so as to be partially opposed to eachother. Specifically, the coil substrate 7 a is shifted downward in FIG.7C and the coil substrate 7 b is shifted upward in FIG. 7C to create thespace for arranging the optical path 3.

Therefore, the suspension wires 10 are not in parallel with each other,but are somewhat opened to the direction of the lens holder 5.Specifically, as shown in FIG. 7C, each of the suspension wires 10 isextended to the lens holder 5 at an angle increased by an angle a fromthe direction of the lens holder 5 (that is, the jittering direction J),and the ends of the suspension wires 10 are fixed on the actuator base8. Moreover, as is evident from comparison with FIG. 7B, the fixingpositions 31 and 32 of the suspension wires 10 to the actuator base 8are shifted by a distance L in the jittering direction J. Namely, a lineconnecting the fixing positions 31 and 32 of the suspension wires to theactuator base 8 is not arranged in parallel with the coil substrates 7 aand 7 b. The reason is as follows. Since the supporting positions of thesuspension wires 10 on the side of the lens holder 5 are arranged atdifferent levels with respect to the jittering direction J, when thesupporting positions of the suspension wires 10 on the side of theactuator base 8 are not shifted in the jittering direction J, the foursuspension wires 10 cannot have equal length, thereby breaking therelation between the center of gravity of the lens holder 5 and thespring constants of the four suspension wires 10. In order to preventthis problem, the supporting positions 31 and 32 of the suspension wires10 on the side of the actuator base 8 are shifted in the jitteringdirection J and the four suspension wires are made equal in length.

Moreover, when suspension wires of equal lengths are used, the number ofcomponents can be reduced, thereby reducing the product cost. However,it is not always necessary to have suspension wires of equal lengths andvarious lengths are applicable. In that case, the configuration can bemade by suitably setting spring constants and the like of the suspensionwires.

Further, FIG. 7C only shows the two upper suspension wires 10 of thefour suspension wires 10 in the focusing direction. The two lowersuspension wires 10 are held below and in parallel with the two uppersuspension wires 10.

In this way, in the actuator 50 of the present invention, the directionsof the suspension wires 10 are not arranged in parallel but are somewhatopened to the lens holder 5. One of the reasons is that, since the widthof the lens holder is increased in the tracking direction by shiftingthe position of the coil substrates, a spring interval (i.e., theinterval between the supporting wires 10) on the side of the actuator isreduced to have a smaller projection area over the pickup. Anotherreason is that, by providing suspension wires not being in parallel, thespring constant of the suspension wires is increased in a twistingdirection viewed from the arrow 81 of FIG. 3, so that a mode frequency(rolling frequency) in the twisting direction can be higher than aparallel spring. Further, the fixing positions 31 and 32 of thesuspension wires 10 on the side of the actuator base 8 are shifted inthe jittering direction J.

Next, the lens holder will be described below. FIGS. 8A to 8D show theconfiguration of the lens holder 5. FIG. 8A is a top view of the lensholder 5, FIG. 8B is a bottom plan view of the lens holder 5, FIG. 8C isa perspective view of the lens holder 5 obliquely viewed from above, andFIG. 8D is a perspective view of the lens holder 5 obliquely viewed frombelow.

As shown in FIGS. 8A to 8D, the lens holder 5 has a mounting hole 40 formounting the objective lens 4. The mounting hole 40 is shifted from agravity center 41 of the lens holder 5 to the side of the optical path3. The objective lens is normally placed around the center of the lensholder (around the center of gravity of the lens holder, see FIG. 7B).However, in the present invention, the pickup 100 is configured so thatthe coil substrates 7 a and 7 b mounted on the lens holder 5 are shiftedin the tracking direction T to obtain the optical path for directing alaser beam to below the objective lens. Thus, the position mounting theobjective lens on the lens holder 5 is shifted to the optical path 3 ofthe laser beam. Since the optical path 3 of a laser beam has to reachbelow the objective lens 4, when the objective lens 4 is positionedaround the center of the lens holder 5, the optical path 3 of the laserbeam has to reach around center of the lens holder 5. Accordingly, thecoil substrate 7 b on the side of the optical path 3 should be shiftedmore largely to obtain a larger space on the side of the lens holder 5.On the contrary, as shown in FIG. 8A, when the position of the objectivelens 4 (that is, the position of the mounting hole 40) is shifted to theoptical path 3, the optical path 3 is placed closer to the end of thelens holder 5, thereby reducing a shifting amount of the coil substrate7 b on the side of the optical path 3. Hence, it is possible to reducethe length of the lens holder 5.

Moreover, when the mounting position of the objective lens 4 on the lensholder 5 is shifted in the direction of the optical path 3, the centerof gravity of the lens holder 5 itself is shifted to the optical path 3side after mounting the objective lens 4. Therefore, as shown in FIGS.8C and 8D, the configuration of the lens holder 5 is devised as follows.Namely, the wall parts 42 and 43 on the opposite side of the objectivelens 40 of the lens holder 5 are formed with a larger thickness than apart 44 on the side of the objective lens mounting hole 40, for example,and the center of gravity of the lens holder 5 is positionedsubstantially at the center when the objective lens 4 is mounted on thelens holder 5. In this way, the shift of the center of gravity of thelens holder, that may happen by shifting the position of the objectivelens in the direction of the optical path, is cancelled.

Further, as shown in FIG. 8A, the fixing positions 33 and 34 of thesuspension wires 10 to the lens holder 5 have a midpoint substantiallycoinciding with the gravity center 41 of the lens holder 5 supported bythe suspension wires 10. Namely, in FIG. 8A, the suspension wires 10 areeach fixed on the lens holder 5 (to be precise, the coil substrates 7 band 7 a mounted on the lens holder 5) at the fixing positions 33 and 34.In this case, the midpoint of the fixing positions 33 and 34substantially coincide with the gravity center 41 of the lens holder 5.As a result, both ends of the lens holder 5 can be held by thesuspension wires 10 with being equally balanced, thereby preventingrolling and the like of the lens holder 5.

Further, as shown in FIGS. 8A to 8D, the lens holder 5 includes stoppers59, 51 and 52. The stoppers 59, 51 and 52 play a role of limiting thestroke (movable range) of the lens holder 5 in the focusing direction Fand the tracking direction T. Thus, when a focus servo or a trackingservo causes a malfunction, it is possible to prevent the lens holder 5from moving unlimitedly, making contact with the body 1 and the othermembers, and damaging the lens holder 5, the objective lens 4 and so on.

In the lens holder 5 of the present invention, the stopper 59 has bothfunctions of a stopper in the focusing direction F and a stopper in thetracking direction T. Namely, the movement of the lens holder 5 in thefocusing direction F is limited by the stoppers 59 and 51, and themovement of the lens holder 5 in the tracking direction T is limited bythe stoppers 59 and 52.

FIG. 9A shows a state in which the stroke is limited in the focusingdirection F by the stoppers 59 and 51. The stopper 59 (indicated bybroken lines) makes contact with a cover 55 of the body 1 from below andthe stopper 51 similarly makes contact with a cover 56 of the body 1from below, thereby limiting the movement of the lens holder 5 in thefocusing direction F (i.e., the upward direction in FIG. 9A).

FIGS. 9B and 9C show that the stroke is limited in the trackingdirection T by the stoppers 59 and 52. In FIG. 9B, the stopper 59 makescontact with the side wall of a recessed part 57 provided on the body 1.In FIG. 9C, the stopper 52 makes contact with the side wall of arecessed part 58 provided on the body 1. Thus, the moving range of thelens holder 5 is limited in the tracking direction T.

As described above, in the lens holder 5 of the present invention, theposition of the objective lens 4 is shifted in the direction of theoptical path 3. In addition, as well shown in FIG. 8D, the portion ofthe lens holder 5 on the side of the mounting hole 40 of the objectivelens has a relatively small thickness and the portion of the lens holder5 on the opposite side to the mounting hole 40 has a relatively largethickness to adjust the center of gravity of the lens holder 5.Moreover, it is desirable to minimize the number of members provided inthe direction of the optical path 3 around the mounting hole 40 so asnot to interrupt the optical path of a laser beam reaching below theobjective lens 4 from the laser light source 2. For these reasons, thestopper 59 has stroke limiting functions both in the focusing directionF and the tracking direction T.

As described above, according to the actuator of the present invention,the pair of coil substrates mounted on the lens holder is shifted in thelongitudinal direction (tracking direction T) of the lens holder toobtain the optical path for directing a laser beam to the position belowthe objective lens. Thus, it is possible to direct a laser beam to theposition below the objective lens at the same height level as the coilsubstrates and the magnets, thereby reducing the thickness of the wholeactuator.

The invention may be embodied on other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description and all changeswhich come within the meaning an range of equivalency of the claims aretherefore intended to embraced therein.

The entire disclosure of Japanese Patent Application No. 2002-152061filed on May 27, 2002 including the specification, claims, drawings andsummary is incorporated herein by reference in its entirety.

1. An actuator comprising: a lens holder having an upper face forholding an objective lens and a pair of side faces for holding coilsubstrates; the objective lens fixed to the upper face; and the pair ofcoil substrates fixed to the pair of the side faces, wherein theobjective lens is fixed at a position displaced from a center of gravityof the lens holder to one end of the lens holder, and one of the pair ofthe coil substrates is fixed on one of the side faces of the lens holderin a range from the one end of the lens holder to a center portion ofthe lens holder, and the other one of the coil substrates is fixed onthe other one of the side faces of the lens holder in a range from theother end of the lens holder to the center portion of the lens holder.2. The actuator according to claim 1, wherein the lens holder has a massportion at a side of the other end, the mass portion having a masslarger than a mass of the one end of the lens holder.
 3. The actuatoraccording to claim 1, wherein the lens holder comprises a first stopperprovided at the one end and a second and a third stoppers provided atthe other end, the second stopper contacts a portion of a body mountingthe actuator to limit movement of the lens holder in a focus directionof an optical disc, the third stopper contacts the portion of the bodyto limit the movement of the lens holder in a tracking direction of theoptical disc, and the first stopper contacts the portion of the body tolimit the movement of the lens holder in both of the focus direction andthe tracking direction.
 4. The actuator according to claim 1, furthercomprising: an actuator base having a pair of yokes; and a pair ofmagnets fixed to the pair of the yokes, wherein each of the pair of themagnets is positioned opposing to each of the pair of the coilsubstrates.
 5. The actuator according to claim 4, wherein each of thepair of the coil substrates comprises a tracking coil and a focus coilformed in alignment with each other in a horizontal direction of thecoil substrate, and the coil substrates oppose to each other only inareas where the focus coil is formed.
 6. The actuator according to claim5, wherein each of the pair of the coil substrates comprises a pair oflands in an area where the focus coil is formed, and the lens holderfurther comprises connection wires which electrically connect the landson the pair of the coil substrates.
 7. The actuator according to claim4, wherein each of the pair of the magnets comprises a magnetizationpattern having a boundary area, and an north pole area and a south polearea on both sides of the boundary area, a vertically extending portionof the boundary area perpendicularly crosses the tracking coil of thecoil substrate, and a horizontally extending portion of the boundaryarea perpendicularly crosses the focus coil of the coil substrate. 8.The actuator according to claim 1, wherein a part of a side area of thelens holder is not covered with the coil substrates.
 9. The actuatoraccording to claim 8, wherein the part of the side area is positioned ata same vertical level as the coil substrates.
 10. The actuator accordingto claim 1, wherein a space below the objective lens is open to externalvia a side area of the lens holder between the pair of the coilsubstrates.
 11. The actuator according to claim 10, wherein the sidearea is positioned at a same vertical level as the coil substrates. 12.The actuator according to claim 1, wherein the lens holder comprises amounting hole which holds the objective lens and which is shifted from agravity center of the lens holder to a side of an optical path.